The present invention relates to a roll press having a first press roll and a second press roll the principal axes of which lie in a press plane and which form a press nip with each other. The invention proceeds from a roll press having a first press roll and a second press roll which cooperate to form a press nip. The principal axes of both of the press rolls lie in a press plane. Each press roll has a rotatable shell. There are journal pins at both ends of the press rolls. Either a rotatable shell has a rotatable journal pin or a stationary support extends through the roll shell and has stationary journal pins. Both of the press rolls are supported at their journal pins on a respective bearing pedestal for the journal pin. At least one bearing pedestal at one end of one of the press rolls is coupled to the other bearing pedestal at the same end of the press rolls by at least one and more usually by two detachable tension bars. The two tension bars are located at both sides of the press plane, extend substantially parallel to that plane and extend in a direction perpendicular to the principal axes of the press rolls. These features of a press roll are known from U.S. Pat. No. 3,921,514.
In one embodiment of the known roll press, the first press roll is located in the lower position and the second press roll in the upper position. Thus, the bearing pedestals of the first press roll are on a stand, foundation or the like. From U.S. Pat. No. '514, however, the reverse arrangement is also known, in which the bearing pedestals of the first (in this case upper) press roll are suspended from the bottom of a stand. The invention concerns both arrangements. Furthermore, the known roll press is developed in the manner that the bearing pedestals in which the second press roll rests are rigidly attached to the bearing pedestals of the first press roll by tension bars. Said tension bars are developed as screws and, in loaded condition of the roll press, must transmit high tensile forces which result from the pressing force prevailing in the press nip. It must be borne in mind in this connection that such press rolls are used preferably in paper manufacturing machines, the width of which may in extreme cases amount to up to 10 m. Furthermore, certain roll presses (for instance in accordance with U.S. Pat. No. 4,503,765 are developed as shoe presses in which the linear force prevailing in the press nip may reach an order of magnitude of 1000 kN/m.
To be sure, in the case of the object of U.S. Pat. No. '514 the pressing forces are kept away from the machine stand so that the latter must bear at most the weight of the roll press itself. However, there is the problem that said screw connections become extremely bulky and expensive. Furthermore, the screws must be under a considerable initial stress, which, according to U.S. Pat. No. '514, must be greater than the maximum pressing force. In other words: the screws are strongly stressed even in the unloaded condition of the roll press. Therefore, the mounting of the screws can be effected only at enormous expense.
Upon the use of the known roll press in the press end of a paper manufacturing machine, there is the further complication that at least one endless felt belt must pass through the press nip and that such felt belt must be replaced at regular intervals by a new felt belt. For this purpose, it is necessary each time to loosen the said screw connections and then priestess them again after the new endless felt belt has been introduced. These are very cumbersome and time-consuming operations in view of the bulk of the screw connections and the high initial stressing of the screws required.
Another problem in connection with such roll presses is that in the case of each press roll at least one of the two journal pins must be displaceable in axial direction under the full operating load because of the thermally caused changes in length of the rotatable roll shell or the stationary support which at times take place. In the case of a turnable journal pin, therefore the outer ring of the antifriction bearing, for example, must be displaceable in the bearing housing. Or in the case of a stationary journal pin, it must be seen to it, for example, that this journal pin is axially displaceable in a sleeve (or bushing). In both cases, slide surfaces must be provided which are suitable for transmitting the immense press forces and at the same time permit the necessary axial displacement.